For anyone who wishes to see something truly spectacular Grand Prismatic Spring in Yellowstone National Park, Wyoming should be on the list. The hot spring is the third largest in the world, and the largest in the United States. For visitors to reach Grand Prismatic Spring one must drive to Midway Geyser Basin. This basin is located on the same loop at Old Faithful.

The spring was first found by European explorers in 1839. They were part of the American Fur Company walking through the country to find animals to trap for fur. One of the explorers made a note of the "boiling lake'' stating its diameter was 300 feet. In 1870 the lake was truly made noteworthy when the Washburn-Langford- Doane Expedition entered the area. They also wrote about the area noting the 50 foot Excelsior Geyser, which is nearby.

Visitors who have seen images of Grand Prismatic Spring in Yellowstone may wonder what provides such brilliant colors. The water is a vibrant blue, with red color like lava surrounding it. However, what looks like lava is actually pigmented bacteria. They form microbial mats around the edge of the water. The bacteria are not all red though. It can range from green to red depending on the chlorophyll and carotenoids provided. The temperature can also determine what color the bacteria favors.

For instance in summer the mats will be orange and red. In winter they are often a dark green. The mats do not form in the center of the spring because the water is a great deal hotter. The bacteria are unable to grow. The blue water of the spring is brought about partly from the high purity and depth of the spring.

Grand Prismatic Spring is 250 feet by 300 feet. It is 160 feet deep. Each year the spring will discharge about 560 gallons per minute at a temperature of 160 degrees Fahrenheit. The water temperature can vary from 147 to 188 degrees F during the year. The temperatures, of course, make it impossible to swim in the spring. The water gets its heat from underground vents as part of the volcanic system that Yellowstone sits on. Instead of forming a geyser over the area, the land parted enough to make the spring.

Visitors who wish to see Grand Prismatic Spring will find the entrance to the spring closest to the west entrance of the park. Visitors can pay $25 per vehicle or $12 per person to enter the National Park and explore the entire park. At Grand Prismatic Spring there is a wooden walkway that takes visitors over the earth, close to the bacteria and spring to get a truly decent view of it. Photos can be taken on the walkway with the steam rising from the spring and the orange bacteria edging closer to the walkway. Surrounding the spring are small rolling hills and mountains. These are in the distance and littered with pine trees adding lush green colors to the view of the spring.